1. Field of the Invention
The present invention relates to a wet chemical treatment method in which the treating (the etching or the wet cleaning) of a semiconductor substrate is carried out in a manufacturing process of semiconductor devices or the like.
2. Description of the Prior Art
In the case of a typical wet cleaning method of a semiconductor substrate in which a cleaning fluid containing aqueous ammonia and aqueous hydrogen peroxide is used, the cleaning fluid is heated up to about 60.degree. C. and the semiconductor substrate is cleaned, and the concentrations of chemical components in a treatment bath change with time toward their decrease owing to the evaporation, the decomposition and the like of the chemicals.
A conventional wet cleaning machine, as shown in FIG. 5, is provided with a storage tank 105 for storing aqueous ammonia, a storage tank 106 for storing aqueous hydrogen peroxide and a storage tank 107 for storing pure water, and required amounts of aqueous ammonia, aqueous hydrogen peroxide and pure water are fed from these storage tanks 105, 106 and 107 to a treatment bath 101 by the driving of solution feed pumps 108, 109 and 110. Next, in the treatment bath 101, a semiconductor substrate (not shown) is cleaned. Reference numeral 102 is a circulating pump of the treatment bath, and numeral 103 is its filter. In this case, aqueous ammonia and aqueous hydrogen peroxide are automatically replenished to the treatment bath 101 every predetermined amount at a certain time interval.
In this method, however, it is difficult to constantly keep the concentrations of the respective chemical components in the treatment bath 101, and in the case that the method of an automatic replenishment is not optimized, the concentrations of the respective drug solutions noticeably change with time, so that the scattering of the concentrations increases inconveniently.
In order to constantly keep the concentration of the cleaning fluid in the treatment bath, as shown in FIG. 6 of Japanese Patent Application Laid-open No. 278529/1992, a wet cleaning machine is used in which an ammonia component analyzer 161 for measuring the concentration of ammonia and a hydrogen peroxide component analyzer 162 for measuring the concentration of hydrogen peroxide are attached to a treatment bath 151, and the concentrations of ammonia and hydrogen peroxide in the cleaning fluid are separately monitored via a filter 154, a solution feed pump 153 and open-close valves 163, 164. On the basis of signals from the component analyzers 161, 162, open-close valves 155a, 156a disposed in the storage tank 155 for storing ammonia and the storage tank 156 for storing hydrogen peroxide are controlled to automatically replenish the chemical treatment fluid whose concentrations decrease, whereby the concentration of the cleaning fluid can be constantly kept up.
Furthermore, the concentration decrease of hydrogen peroxide is usually slighter, as compared with the concentration decrease of ammonia by evaporation and the like, and therefore, Japanese Patent Application Laid-open No. 259141/1993 has disclosed a method in which aqueous hydrogen peroxide is not replenished and aqueous ammonia alone is replenished in accordance with a treatment temperature.
In all of the above-mentioned conventional techniques, much attention is paid to the control of the composition. Needless to say, if the composition is constantly kept, a wet-chemical treatment ability can be constantly maintained, but in Japanese Patent Application Laid-open No. 142435/1995, it has been disclosed that as long as the wet cleaning is carried out in a concentration region in which an etching rate to an ammonia concentration scarcely fluctuates, the wet-chemical treatment ability can be maintained, even if the composition is not always strictly constantly kept.
Japanese Patent Application Laid-open No. 142435/1995 has disclosed a method in which the wet cleaning is carried out in the concentration region in which the etching rate to the ammonia concentration scarcely fluctuates, and another method comprising a combination of this method and a method in which a concentration control is carried out by measuring the concentrations of the chemical components or a method in which ammonia alone is replenished.
In a method disclosed in Japanese Patent Application Laid-open No. 278529/1992 in which the treatment is carried out, keeping the composition of the chemical treatment fluid constantly, the chemical containing the chemical component of which concentration largely fluctuates by volatilization and decomposition is replenished in order to keep the concentration of the chemical component, and at this time, the other chemical components are diluted with this replenishment. In consequence, the other chemicals containing the other chemical components must also be replenished. Therefore, the large amounts of the chemicals which are to be fed to the treatment bath are required. That is to say, in order to constantly keep the concentrations of the respective chemical components, the replenishment of the large amounts of the chemicals is necessary in addition to the strict concentration control.
The methods of Japanese Patent Application Laid-open No. 259141/1993 and Japanese Patent Application Laid-open No. 142435/1995 are measures devised to deal with the problem of the method of Japanese Patent Application Laid-open No. 278529/1992, but these methods are applicable techniques only under predetermined cleaning conditions. In the disclosed methods, it is difficult to accomplish the cleaning under the above-mentioned conditions sometimes, depending on an object to be cleaned.
In the case of the chemical treatment fluid containing ammonia and hydrogen peroxide, chemical species such as NH.sub.3, NH.sub.4.sup.+, H.sub.2 O.sub.2, HO.sub.2.sup.-, H.sup.+, OH.sup.- and H.sub.2 O are present. Moreover, in the chemical treatment fluid which is cleaning an silicon substrate, there is a pollutant on the surface of the substrate, and chemical species produced by the reaction of the pollutant and the chemical species of the fluid. The cleaning performance of the chemical treatment fluid during the cleaning process depends on the concentrations of the various chemical species, reaction rates and free energies of the chemical reaction in which the above-mentioned chemical components relate, a treatment temperature and the homogeneity of the concentrations of the chemical species in the treatment bath.
However, conventional techniques such as the above-mentioned disclosed techniques are limited to the control of the concentrations of the chemical components, and decision factors of cleaning ability, particularly the concentrations of the dissolved chemical species and the reactions of the chemical species have not been sufficiently controlled. With the high integration of semiconductor devices, it is becoming necessary to strictly control the cleaning ability of the chemical treatment fluid in order to obtain a high reliability and yield of the semiconductor devices. In addition, from the viewpoint of the increase in consciousness of environmental problems on a global scale at present, the reduction of an environmental load by manufacturing, i.e., the amounts of chemicals to be used is desired.